Oil converter



Nov. l, 1932. A. E. HARNSBERGER OIL CONVERTER Filed Jan; 25, 1930Patented Nov. 1, @1932 UNITED STA rss PATENT oFFl'cE AUDLEY E'.HARNSBERGER, OF CHICAGO, ILLINOIS,4 ASSIGNOB T0 G-YRO PROCESS COMPANY,0F DETROIT, MICHIGAN, A CORPORATION 0F MICHIGAN on. CONVERTER.

Application led January 25, 1930. Serial No. 423,521).

This invention relates to improvements in converters of the characteremployed in connection with oil cracking processes, and an outstandingobject thereof resides in the provision of a converter wherein isprovided a plurality of advantageously arranged tube banks, throughwhich the oil to be heated and converted is passed in a vaporous state,and wherein the arrangement of the tube banks is such as to provide forthe eiiicient heating of theoil vapor to cracking or conf versiontemperatures and the maintenance of the vapors at such temperatures fordesired periods of time, ,whereby there is secured from the oil vaporpassed through the tube bank a maximum yield of the desired end productand minimum quantities of undesired fractions such as fixed gas andrecycle stock.

In vapor phase crackin-gef hydrocarbon oils, as the temperature of thevapors increases they expand in laccordance with known laws and as thepressure of the vapors decreases, due, for example, to, frictional drop,the volume also increases. It is desirable to heat the vapors whenfirstintroduced into the converter rapidly until the vapors attain a crackingtemperature and to then decrease the quantity of heat suppliedv to thevapors to maintain the latter at a substantially constant temperatureduringthe cracking period. To secure satisfactory tube life at positionsof` highest heat input it is necessary to employ high vapor velocitiesin order to conduct away the heat from the metal walls of the tubes. Ifthe velocity is not high, the tube reaches a very high ternperature,approaching that of the actual furnace temperature, which results inshort life of the tubes. Therefore, high vapor velocity is necessary atthe points of highest heat input, but as the cooler zonesI of thefurnace are reached the-.vapor velocity can be safely reduced, or if notreduced at least held constant, and this factor permits of the use oflarger tubes in the cooler cracking zone to compensate for the increasein volume dueto increased temperatures and reduction in pressure. Again,at the point in the converter Where cracking takes place there isliberated acertain amount of so-called fixed gases, which also greatlylincrease the volurne of material passing through the cracking coils,and in these portions of the coil if increased flow or tube area is notprovided, undesirably high frictional resistance will be encountered,which the present invention avoids.v

Itis, therefore, another object of the present invention to provide aconverter for cracking oil in the vapor phase, and wherein use is madeof a cracking coil provided with increased cross-sectional or tube areaat various .points throughout the unit or coil to provide, first, forhigh velocity of oil vapor flow at the entrance portion of the coil and,sec- 0nd, for gradually increasing vapor crosssectional area toward thedischarge or outlet end of the coil.

For a further understanding of the invention reference is to be had tothe following description and the accompanying drawing,

wheren:

Figure 1 is a vertical sectional'view taken through a converterconstructed in accordance with the present/invention, and

Figure 2 is a transverse cross-sectional view on the line 2-2 of Figure1.

Referring more particularly to the drawing, the numeral 1 designates asettin of the furnace or converter. The interior o the latter isprovided with a transversely extending bridge wall 2 which divides, thesetting* internally into combustion and tube chambers 3 andrespectively. The combustion chamber is provided with burners 5 fordeveloping highly heated furnace gases, the latter passing generallyupwardly through the combustion chamber and then sweep horizontallyalong the roof of the furnace and turn substantially downwardly formovement through the tube chamber 4. 'The lower portion of the tubechamber is provided with a horizontally'directed duct V6whichcommunicates with a vertically disposed stack 7 tllrough which thegases escape to the atmosere. A p Arranged in the duct 6 is a bank 8 ofoil vpreheating or vaporizing tubes. This bank of tubes is preferablyheated by the waste gases discharged from the chamber 4, a feature whichpermits of the eiicient utilization of the heat developed by the furnaceso that the gases discharged from the stack 7 will be of a minimumtemperature. The charging stock enters the bank of tubes 8 by wa of aline 9, and is forced serially through the tubes of said bank in orderthat the oil may be heated to a vaporizing temperature of approximately700 to 750 F. Ordinarily little orv no crackingpof the oil takes placein the tube bank 8, and preferably, the charging stocks delivered to thevaporizing tubes comprise a clean fraction of as oil boiling range fromwhich carbon pro ucing high boiling oils have been removed.

The oil discharged from the bank 8 passes by way of the pipe line 10 toan evaporator 1l, wherein the hi h boiling point oils, which remain inthe liquid state at the temperatures specified, are dropped to thebottom of the evaporator and withdrawn by way of the valved outlet 12.These high boiling oils may be disposed of as fuel oils. The lighteroils which are in a vaporized condition in the evaporator 11, passoverhead from the latter by way of the outlet line 13 and are deliveredto a series of drying tubes 14 arranged in the low temperature side ofthe tube chamber 4. Superheated steam may be introduced'into the outletline 13 by way of the steam line 15 in desired quantities. p The dryingtubes 14 are of relatively large cross-sectional area, for example,eight inches in diameter, and the oil vapors fiow serially through theseveral tubes comprising the row 14, whereby the vapors are heated to adry substantially gaseous condition and liquid oils effectually removedtherefrom. Some carbon deposit may take place in the tubes 14, but owingto the large cross-sectional area of these tubes such deposits will havelittle or no practical effect on the transmission of heat to the vaporsor in the matter of seriously obstructing oil vapor How through thetubes.

Afterthe vapors have been dried by passage through the tubes 14 they arecontinuously transmitted to a bank of cracking or converting tubes 16,consisting of a plurality of serially connected pipes or tubes, whichare arranged in the radiant heat zone of the combustion chamber 3 andare disposed preferabl around the sides and top walls of the cham er 3.In the operation of systems of this kind it is desirable to raise thetemperature of the oil vapors which enter the conversion zone rapidlyfrom a vaporizing or drying temperature of approximately 750 F. to anactive cracking 'temperature in excess of 1000 F. A very practicalmethod of accomplishing this consists in placing the first bank of tubescomprising the cracking section in the radiant heat zone of the furnace,as indicated at 16. It will be understood that therate of heat transferby radi ation-is proportional to the fourth power of the difference''between the absolute temperature of radiating and adsorbing structures,whereas the rate of heat transfer by convection is proportional totheIirst power and the diderence between the absolute temperature of thehot gases and the heat absorbingstructure. Accordingly, where heattransfer is effected simultaneously by radiation and convection, thetemperature of the heat absorbing structure may become excessive.Therefore, to prevent injury to the tubes 16 it is important that thesetubes be kept clear of carbon deposit and the' velocities of oil traveltherethrough maintained at a relatively high point in order that theheat applied to said tubes may be quickly absorbed by the rapidly movingoil vapors and conducted away. The drying tubes serve to eliminatecarbon deposit in the cracking tubes 16, and since the latter are ofrelatively small cross-sectional area the velocity of oil traveltherethrough is high, in excess of 2500 feet per minute. This results inkeeping the Walls of the tubes 16 at a temperature where they will notbe deleteriously affected by the high heat of the furnace.

After the oil has been discharged from the bank of tubes 16 it possessesa temperature in eXcess of 1000o F. and less than 1200o F. Sincecracking is a product of both time and temperature, it is necessaryto-maintain the vapors for a desired period of time at aparticularcracking temperature to secure a de- Vsired rate of conversion. Carefulregularelatively placed to secure a uniform appli-I cation of heatthereto at given temperatures to overcome unequal heating of the oilvapors which'lpass through the tubes.

In the attainment of these ends the chamber 4 is provided with ahorizontally placed row of tubes 17, which are located in the upperportion of the chamber 4 and are subjected to a high degree offurnaceheat, which is of such a character that the oil vaporsdischargedfrom the tubes 16 and then passed serially through the tubes 17 arebeing constantly and uniformly heated. This rate of heat input is suchas to more than overcome loss of heat due to the endothermic reactionstaking place in the oil vapors while the latter are undergoing cracking.From the tubes 17 the oil vapors flow serially pors are passed seriallythrough a third row of tubes 19 which are .disposed between the tuberows 17 and 18. The tubes compris-- ing the rows 17, 18 and 19 areprogressively increased in cross-sectionall a,`rea. This is done inorder to accommodate for the eX- pansion of vapors due to thetemperature rise and also to the drop ,in pressure by reason ofdecreased frictional resistance between the moving oil vapors and thewalls of the tubes. The largest part of this increase in volume isundoubtedly due to the drop in pressure rather than the increase intempera? ture. Thus the oil vapors passing through the tubes 16, 17 18and 19 are constantly heated to secure a continuation of the desiredcracking reactions, but in the tubes 17, 18 and 19 preferably lowervapor velocities obtain over the velocities prevailingin the tubes 16 tosecure the desired time factor in the conversion of the oil. The oilstraveling through the tubes 18 and 19 are heated sulficiently tomaintain the same at a cracking temperature in excess of 1000 F. and itfollows that' these tubes are not to be considered as mere soakingchambers but active heat .applying elements.

rIhe cracked oil vapors discharged from the tubes 19 are introduced intoan arrester 20 where the vapors are brought into direct contact with alarge quantity of cold oil which is sprayed into the arrester. Rapidheat exchange takes place andthevapors are dropped in temperature from1000 F. to a fractionating temperature not in excess of 600 F. /Thissudden drop in temperature results in minimizing the liberation of freecarbon in the act of cooling the vapors. 'The vapors released from thearrester may be fractionated in any suitable Way and s'ubsequentlycondensed for various purposes. The liquids obtained from the bottomJ ofthe arrester may be employed as recycle stock. ln recapitulation itwillbe seen that the vapors introduced into the converter are first A 17will be not greater, but possib y less, than passed through the dryingtubes 14 to insure that no liquids, with its coke-forming tenden-V cies,will be introduced into the high radiantheat zone in which the tubes 16are located. In the tubes 16 high vapor velocities'are maintained inorder to successfully conduct away the heat fromV the metal walls of thetubes and to quickly heat'the vapors to a desired crackinga temperaturein excess of 1000o F. The vapors are then conducted to the tubes 17,which Vpossess greater crosssectional area than the tubes 16 in orderthat thevelocity of vapor flow throu' h the tubes the velocities of flowin the tubes 16, this reduction in velocity serving to decrease therlctionalback pressure of the cracking coils.

The vapors'are then conducted to a still cooler heating zone of thefurnace, namely the tubes 18 and 19, where the vapors having. reached acracking temperature by passage through the bank 17 will be held atsubstantially alconstant Itemperature by supplying only' the heat.necessary to overcome endothermic heatI losses. The tubes and 19 are ofgreater cross-sectional area*V` than the tubes 16 and 17 since in thissection a considerable volume of light products, such as motor fuel andpermanent gas are generated, which cause an increase in volume and itis, therefore, desirable to provide for this in crease in volume by anincrease in crosssectional area, -so that high frictional back pressurewill not be set up in this portion of the converter where highvelocities on account of heat transfer are not required. The conversionreactions having been completed in the tubes 18 and 19 are suddenly andsubstantially' instantaneously arrested by the operation of the unit 20.

4 In order to demonstrate the necessity for providing for increase incross-sectional area in various heating portions of thev converter onaccount of the change that takes place in the vapors as they travelthrough the converter, the following table is given:

From the above it will be noted that in a representative converter thedrying section 11 will be made of tubes having an internal diameter ofeight inches, permitting low velocity and 'very slight friction loss.At.

thispoint volume is desirable in order to provide space for theformation of such coke that is produced during the drying operation. Itis desirable to have suflicient volume in the tubes 14 to provide forextended converter runs Without shutdowns for cleaning purposes.However, as soon as the tubes 16 are reached the tube size is reduced tofour inches in diameter in order to provide high vapor. velocities whichwill insure heating the vapors in the minimum of time and, also, thatthe tube Walls will remain at a safe operating temperature under furnacetemperatures of i2000o 4to 2400" F. In .the tube bank 17 a siii inchdiameter tube is em'- ployed in order that there will not be a largeincrease in velocity of the vapors and consequently back pressure on theevaporator 11. The vapors, beinglighter, will not have the same heatabsorbing capacity in the section 17 as in the section 16.' However, at.this point the furnace temperature is reduced to approximately 180091?.and, therefore, the tube walls will not reach an excessive teniperature.In the tube rows 1S and 19 the size ofthe tubes will be again increasedin order to provide a sufficient time factor and at the same timeprevent back pressure by preventing excessive vapor velocities.v Thevapor velocity in this latter section will be considerably decreasedsince the tubes at this point receive a very low rate of heat transferby convection from the flue gases, which will be in the neighborhood of1500o F. The lue gases are then transferred to the outlet duct 6, wherethey are 'used to heat or vaporize the charging stock passing throughthe tubes 8, after which the gases may escape to the atmosphere by the outlet stack 7.

What is claimed is:

1. In a converter for cracking hydrocarbons in the vapor phase, asetting formed with an internal bridge wall which divides the settinginto combustion and tube chambers, the latter being in relative opencommunication over the top of the bridge Wall, burner mechanism arrangedin said combustion chamber, an outlet duct in communica.

tion with the lower part of the tube chamber, a bank of drying tubesarranged in the lower part of the tube chamber, means for supplyingvaporized oils to said drying tubes, a bank of cracking tubes arrangedin said combustion chamber, said cracking tubes possessing across-sectional area materially less" than that of the drying tubes,means for passing oil vapor from'the drying tubes to the cracking tubes,and a second bank of cracking tubes arranged in said tube chamber andthrough which the vaporized oils are passed following their passagethrough said first named cracking tubes, the cracking tubes in said tubechamber being individually of greater cross-sectional area than theindividual cracking tubes in the combustion chamber but `of lesscross-sectional area than the individual drying tubes.l

2. In a converter for cracking hydrocarbons in the vapor phase, asettingformed with an internal bridge Wall which divides the settinginto combustion and tube chambers, the latter being in relative opencommunication over the top of the bridge wall, burner mechanism arrangedin said combustion chamber, an outlet duct in communication with thelower partiof 'the tube chamber, a bank of drying tubes arranged in thelower ing vaporized oils to said drying tubes, a bank of cracking tubesarranged in saidcombustion chamber, said cracking tubes possessing across-sectional area materially less than that of the dryingtubes,means, for passing oil vapor from the drying tubes to the crackingtubes, a second bank of cracking tubes arranged in said tube chamber andthrough part of the tube chamber, means for supply-V

